Magnetic system for electrodynamic transducers



Jan. 3, 1967 H. FANSELOW 3,296,386

MAGNETIC SYSTEM FOR ELECTRO'DYNAMIC TRANSDUCERS Filed Dec. 29, 1964United States Patent Ofifice 3,295,386 Patented Jan. 3, 1967 3,296,386MAGNETIC SYSTEM FOR ELECTRO- DYNAMIC TRANSDUCERS Heinrich Fanselow,Landshut, Bavaria, Germany, assignor to International Standard ElectricCorporation Filed Dec. 29, 1964, Ser. No. 421,900 Claims priority,application Germany, Jan. 8, 1964, St 21,526 3 Claims. (Cl. 179-120)This invention relates in general to electro-dynamic transducers and inparticular to telephone receivers. Magnetic systems equipped withcylindrical or annular-shaped magnetic insets of alloyed steel ascarriers of the magnetic energy are used in such dynamic transducers.The iron parts of the magnetic system forming the magnetic circuit orflux path are shaped so that they leave an operating air gap in which acoil moves in the rhythm of the sound. In other known magnetic systemsannular,

ceramic magnetic insets are used to carry the magnetic energy. Themagnetic flux in such systems are led via pole plates and a pole coreinto the operating air gap.

A drawback of the above described magnetic systems used for dynamictransducers is their relatively high weight which, for example, isdisadvantageous when the dynamic transducers with annular magneticinserts are used in telephone receivers. A weight reduction can beobtained by using smaller magnetic rings and consequently, smaller poleplates. This reduction in weight, however, causes a loss of magneticenergy and correspondingly reduces the degree of the acoustic effect.

Thus, an object of the invention is to provide new and uniqueelectro-dynamic transducers.

A related object is to provide light weight electrodynamic transducershaving improved frequency characteristics.

A further object is to provide improved, relatively inexpensive, lightweight transducers using magnetic elements made of sintered iron.

According to the invention the noted drawbacks are avoided in that themagnetically conductive parts, required to form an operating air gap inthe magnetic system, such as pole plates and pole cores, consist ofsintered iron and that these parts with the magnetic inset as carrier ofthe magnetic energy are composed by gluing or other composing methodsknown to the art. The reduced specific weight of such parts, made ofsintered iron, results in a weight reduction compared with solid iron.In addition, the porosity of the sintered material aids in dampening thedeleterious resonant peaks. Despite the smaller specific weight of partsmade of sintered iron, the magnetic conductivity of said partsincreases. This increase of the magnetic conductivity acts to furtherreduce the weight of the pole plates and the pole core according to afurther embodiment of the invention by reducing the thickness of thepole plates towards the periphery and by allowing a cavity to be boredin the pole core, without undergoing a loss of magnetic energy. Due toan annular stud of little height around the pole core, the externaldiameter corresponds to the internal diameter of the ferrite ring. Themagnetic losses which occur at the transition between the lower poleplate and the pole core, due to an increased scattering of the magneticflux lines is further reduced, resulting in an increase of the air gapinduction. Another advantage of the described annular stud of the poleplate is the saving of a center adjusting ring, when using sintered ironwhich has, besides the costs of material, no further expenses.

The use of sintered iron for the iron parts forming the magnetic circuitflux renders financial advantages despite the increased price for thebase material, because a final treatment is not required.

The above mentioned and other features of this invention and the mannerof obtaining them will become more apparent, and the invention itselfwill be best understood by reference to the following description of anembodiment of the invention taken in conjunction with the accompanyingdrawing.

The accompanying drawing shows a preferred example of a dynamictransducer for telephone sets with the arrangement of such a magneticsystem. An annular body 1 of ceramic magnetic material is provided tocarry the magnetic energy. The top pole plate 2 has a cross-sectiondecreasing in thickness towards the periphery and an annular study 2awhich serves for centrally fixing of the basket-like diaphragm carrier4. The bottom pole plate and the pole core 3 are manufactured in oneproduction process. The annular study 3a around the pole core, providedfor centering, is clearly seen on the drawing. The basket-like diaphragmcarrier 4 can be connected with the top plate 2 by riveting. In the airgap 5, formed by the pole hole of the top pole plate 2 and the pole core3, a coil freely oscillates. A cavity 6, obtained in this pole core, canbe made a resonator, if the cover 7, which closes the opening airtight,and an attenuating disk 8 exist, which disk can be used as an acousticfilter for connecting the adjacent air spaces.

While the principles of the invention have been described above inconnection with specific apparatus and applications, it is to beunderstood that this description is made only by way of example and notas a limitation on the scope of the invention.

I claim:

1. A magnetic system for electro-dynamic transducers comprising a coreof sintered magnetic material, a bottom pole plate which decreases inthickness towards the periphery thereof and is integral to said core, atop pole plate which decreases in thickness towards the peripherythereof and is fabricated of sintered magnetic material, said top poleplate associated with said core to form an operating air gap in saidmagnetic system, a stud centrally arranged around the air gap, abasket-like diaphragm support accommodated by said stud, and an inset ofmagnetic material located between said pole plates, surrounding saidcore.

2. The magnetic system of claim 1, wherein the lower pole plate isprovided with a centrical stud around the pole core which serves tocenter said magnetic inset.

3. The magnetic system of claim 2, wherein a cavity is bored throughsaid core, cover means are provided for closing off the bottom of saidcavity and an attenuating disk is provided at the top of said cavity,whereby said closed cavity acts as a resonator.

References Cited by the Examiner UNITED STATES PATENTS relied upon.

KATHLEEN H. CLAFF Y, Primary Examiner. ROBERT H. ROSE, Examiner. F. N.CARTEN, Assistant Examiner.

1. A MAGNETIC SYSTEM FOR ELECTRO-DYNAMIC TRANSDUCERS COMPRISING A COREOF SINTERED MAGNETIC MATERIAL, A BOTTOM POLE PLATE WHICH DECREASES INTHICKNESS TOWARDS THE PERIPHERY THEREOF AND IS INTEGRAL TO SAID CORE, ATOP POLE PLATE WHICH DECREASES IN THICKNESS TOWARDS THE PERIPHERYTHEREOF AND IS FABRICATED OF SINTERED MAGNETIC MATERIAL, SAID TOP POLEPLATE ASSOCIATED WITH SAID CORE TO FORM AN OPERATING AIR GAP IN SAIDMAGNETIC SYSTEM, A STUD CENTRALLY ARRANGED AROUND THE AIR GAP, ABASKET-LIKE DIAPHRAGM SUPPORT ACCOMMODATED BY SAID STUD, AND AN INSET OFMAGNETIC MATERIAL LOCATED BETWEEN SAID POLE PLATES, SURROUNDING SAIDCORE.